1. Field of the Invention
The present invention relates to a variable turbocharger and a control method for the same. More particularly, the present invention relates to a variable turbocharger and a control method for the same that may prevent turbo lag at a low speed and be highly efficient at a high speed.
2. Description of Related Art
In a conventional internal combustion engine, negative pressure generated during an intake stroke induces a mixture of air into a cylinder. This is called natural aspiration or normal aspiration. However, a valve opened time is too short to sufficiently intake the air mixture, so forcible pumping is used for enhancing the volume effect of a cylinder, effective pressure ratio, and explosion pressure, thereby improving output. This is called turbocharging, and an apparatus for turbocharging is called a turbocharger.
A conventional turbocharger 105, as shown in FIG. 1, includes a turbine 101 and a compressor 103, and is connected with an exhaust manifold 109 of an engine 107 for receiving exhaust gas.
The compressor 103 intakes air from an air cleaner 111 via an intake pipe 119, and the air is cooled in an intercooler 113 and supplied to the engine 107 via an intake manifold 115.
The turbine 101 is connected with an exhaust pipe 117 exhausting the exhaust gas.
Thus, rotation of the turbine 101 induced by the exhaust gas of the engine 107 turns the compressor 103 connected with the turbine 101 by a shaft 121 and the cooled and compressed air is supplied from the air cleaner 111 to the intake manifold 115.
FIG. 2 shows a partial cross-section of a conventional turbocharger, and shows a turbine housing 123 provided with an inlet 122 into which the exhaust gas flows.
The turbine 101 that is connected with the compressor 103 by a shaft 121 is disposed within the turbine housing 123.
The characteristics of the turbine 101 are determined by an A/R ratio, wherein A indicates a cross-section of the inlet 122, R indicates a distance between the center of the turbine 101 and the center of the cross-section of the inlet 122, and the A/R ratio means a value of A divided by R. If the A/R ratio is small, the turbine 101 is sensitive to acceleration and resisting force to exhaust tends to be increased at a high speed.
A conventional A/R ratio is 0.5-1.0. The lower the A/R ratio, the faster the turbocharging is at low RPM, but performance is deteriorated at high RPM.
That is, when the A/R ratio is high, turbo lag may be occurred at low RPM, however output is improved at high RPM.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.